1. Field of the Invention
This invention relates to a novel unsaturated polyester compound which can be advantageously used as a photocuring component and/or thermosetting component in various field of application, an alkali-soluble and actinic energy ray-curable resin obtained therefrom, and processes for the production thereof.
This invention further relates to a curable composition which contains the unsaturated polyester compound mentioned above and hardens promptly by irradiation of an actinic energy ray such as an ultraviolet ray or an electron beam or further hardens by heating to give a cured product exhibiting high flexibility (flexing resistance) and strength in combination and excelling in adhesiveness to a substrate. More particularly, this invention relates to an actinic energy ray-curable resin composition which contains the actinic energy ray-curable resin mentioned above and is capable of producing a coating film which can be developed with an aqueous alkaline solution and excels in resistance to heat, electrical insulation properties, adhesiveness, etc.
2. Description of the Prior Art
The curing of resin by irradiation of an actinic energy ray is widely utilized in painting of metal, coating of wood, printing ink, electronic materials, etc owing to its high curing speed. A photocurable composition used in these technical fields generally comprises an unsaturated double bond-containing prepolymer, a polymerizable monomer, and a photopolymerization initiator as essential components. As the above-mentioned prepolymer mainly used as a photocuring component, a polyester acrylate, a urethane acrylate, and an epoxy acrylate may be cited. Since these prepolymers contain polymerizable unsaturated groups therein, they can be cross-linked by mixing with a compound which generates radicals by irradiation of an actinic energy ray (photopolymerization initiator).
However, since a polyester acrylate has substantially no polar group such as hydroxyl group in its side chain, it can not be subjected to a further modification reaction. On the other hand, although a urethane acrylate excels in adhesiveness to a substrate, its usage is limited because it has a urethane linkage which is poor in heat resistance. An epoxy acrylate is most excellent in physical properties and used in various application fields. However, at present the composition containing this compound is inferior in the adhesiveness because it has mainly secondary hydroxyl groups.
Further, since the radically polymerizable prepolymers mentioned above generally has a small molecular weight and cures in an instant by irradiation of an actinic energy ray, thereby causing residual stress in the cured product, they pose the problem of decreasing the adhesiveness to a substrate and mechanical properties. For the purpose of solving such problems, the composition which employs the cationic polymerization of oxetane as a curing reaction has been proposed. However, the kinds of materials which can be used in this reaction are small in compared with radically polymerizable prepolymers or monomers, it was possible to attain the desired properties of the cured product only with difficulty.
Meanwhile, as to the practical application of a curable composition, for instance, in the soldering process which is carried out in mounting electronic parts on a printed circuit board, a solder resist is used for the purpose of preventing molten solder from adhering to irrelevant portions and protecting circuits. In recent years, a developing type solder resist which is used to form a pattern by a photolithographic method is widely adopted. Particularly, with due respect to the problem of environmental safety and from the viewpoint of cost, the solder resist of the alkali developing type has come to play the leading role. As a base resin used for these developing type solder resists, a photosensitive resin obtained by the reaction of an epoxy resin with (meth)acrylic acid and the subsequent reaction of an acid anhydride with the resultant hydroxyl group of the modified resin is generally used.
In recent years, in consequence of the trend of IC and LSI parts toward highly dense mounting, the necessity of decreasing the width of circuit lines and the intervals between circuits of the printed circuit boards has been finding growing recognition. Besides, since the operating frequency of these parts to be mounted is enhanced, the heat value released from these parts increases accordingly. Therefore, the printed circuit board tends to require high thermal stability more than desired heretofore. In the photosensitive resin obtained by using an epoxy resin as a starting raw material, however, since most of the functional groups which bond to an acid anhydride are secondary hydroxyl groups, the resin has the problem of relatively easily suffering the breakage of bonds when exposed to an increased temperature for a long time and, as result, inducing the possibility of degradation of such properties as insulation properties and resistance to heat and contamination of circuits due to the scattering of the decomposed acid anhydride. In the photosensitive resin obtained by using a cresol novolak type epoxy resin as a starting raw material, its cured product is hard and brittle. Accordingly, the application of the resin is restricted because of the possibility of causing cracks during the step of heat cycle, and the resin can not be applied to a flexible circuit board.
To solve such problems, for example, published Japanese Patent Application, KOKAI (Early Publication) No. (hereinafter referred to briefly as “JP-A-”) 2000-159858 discloses a photosensitive resin obtained by the reaction of an epoxy resin with an unsaturated monocarboxylic acid and further with a special acid anhydride. Further, JP-A-2000-321765 discloses a photosensitive resin obtained by the addition reaction of an epoxy resin with a mixture of an unsaturated monocarboxylic acid and a saturated monocarboxylic acid and subsequent modification with an acid anhydride. In either case, however, since the starting raw material is an epoxy resin, it is difficult to improve the hard and brittle natures of the epoxy resin. Accordingly, the problems heretofore pointed out have not been solved yet.
In recent years, from the viewpoints of creation of a new organic reaction and its application to the synthesis of macromolecular compounds, the organic synthesis involving the ring opening addition reaction of an oxetane ring which is an ether of four-membered ring has been studied. For example, the addition reaction of an oxetane compound and an active ester (T. Nishikubo and K. Sato, Chem. Lett., 697 (1992)) and the synthesis of polyester having a primary hydroxyl group attached to a side chain thereof by the polyaddition reaction of a polyfunctional oxetane and a dicarboxylic acid (T. Nishikubo, A. Kameyama, and A. Suzuki, Reactive & Functional Polymers, 37, 19 (1998)) have been studied and reported.
Further, JP-A-10-168120 discloses a method of producing an actinic energy ray-curable resin by the ring opening addition reaction of an oxetane group-containing. (meth)acrylate monomer with a carboxyl group-containing resin or by the ring opening addition reaction of an oxetane group-containing resin with a carboxyl group-containing unsaturated monomer.
However, none of the published literatures mentioned above discloses the compounds of the present invention, actinic energy ray-curable resins obtained therefrom, and a curable composition using them.